Can't register to push notifications (Unity3d - Android)

I followed this setup guide: https://www.pushwoosh.com/programming-push-notification/android/android-additional-platforms/unity-integration/ to implement push notifications in my Unity3d game. When build (for Android) and installed it on a phone, the registration to the Pushwoosh application (CClash - 1F2A4-1F4C8) never goes through - neither of the two callbacks is ever called (onRegisteredForPushNotifications, onFailedToRegisteredForPushNotifications). Are the instructions you provided in the guide sufficient to get push notifications working or is there something that I have missed here?

One other thing: I tried to validate the AndroidManifest.xml and received an error: invalid format for PW_PROJECT_ID when having "A" in front of an ID. Without it, everything went through smoothly. What is going on here?